1. Field of the Invention
The invention relates to a transmission module, especially a transmission module in countershaft design.
2. Description of Related Art
Transmission modules in countershaft design are known from a large number of configurations from the state of the art. They comprise at least one input and one output, between which are arranged speed-torque converter devices which are driven via a countershaft transmission which is torsionally rigidly connected at least indirectly with the transmission input. Reference is hereby made in lieu of the above to the following specifications:    FR 2 719 355 A1    DE 949 990 C
For changing the direction of travel, a reverse gear is usually provided which is also arranged in countershaft configuration and is situated as, seen in the axial direction, downstream of the individual speed-torque converter devices between transmission input and output. The reverse gear is arranged in the simplest of cases by providing an additional intermediate gear in analogy to the individual speed-torque converter devices. A reversal of the direction of rotation is enabled via the intermediate gear.
Such transmissions are usually of a relatively large size, especially with respect to their axial overall length. In addition, they usually also comprise a hydrodynamic retarder arranged on the transmission output or in the transmission for producing a braking torque. It is preferably arranged as a secondary retarder. The rotor blade wheel of the hydrodynamic retarder is preferably coupled with the output of the transmission module and flanged on the housing or integrated in the housing of the transmission module. The rotor blade wheel is directly connected with the output shaft in a torsionally rigid manner or in a high gear. This leads to the consequence however that when discharging the retarder in non-braking operation, the ventilation losses are very high as a result of the continual rotation of the rotor blade wheel and the revolving of the air masses present in the retarder, i.e. there are loss moments which are not available for drive in the drive train. In order to reduce ventilation losses in non-braking operation, the retarder is arranged in the high gear, i.e. in a side branch of the main drive branch. Reference in this respect is hereby made to DE 44 45 024 A1 which discloses a drive unit with an engine and a transmission and a hydrodynamic retarder. In order to avoid ventilation losses in non-braking operation, the hydrodynamic retarder is provided with a configuration so as to be activated in braking operation and is uncoupled from the same when necessary without any influence on the power flow in the main drive branch, with the speed of the rotor blade wheel being reduced to zero in non-braking operation. The arrangement in high gear is used in order to produce only low ventilation losses by the transmission into fast in non-braking operation in the case of uncoupling of the rotor blade wheel that has not occurred or was not intended. The high gear is integrated as a separate spur wheel set on the transmission and thus leads to an increase in the required number of components and the overall space because the same needs to be provided separately.
Reference is hereby made to the following specifications concerning the further state of the art:    DE 197 51 776 A1    WO 86/02608 A1    DE 103 34 731 A1    DE 198 37 776 A1    DE 198 40 288 A2    DE 34 15 909 C2